NRXN1 and schizophrenia: The only example of a single-gene schizophrenia susceptibility CNV is NRXN1. Consistent with genic pleiotropy, exonic deletions of NRXN1 increase liability to schizophrenia and NDDs, but there is marked heterogeneity in the exons affected and the deletion sizes13, leaving uncertainty as to whether precisely the same mutation can cause schizophrenia and NDD.